University of M’hamed Bougara - Boumerdes Faculty of Hydrocarbons and Chemistry. Lesson n 1: Geophysics Group: STH20 1stsemester What is geophysics? It is a subject of natural science concerned with the physical properties of the earth and its surrounding space environment; and the use of quantitative methods for their analysis. The term “geophysics” sometimes refers only to the geological applications: Earth’s shape; its gravitational and magnetic fields; its dynamics and their surface expression in plate tectonics; the generation of magma; volcanism and rock formation. However, modern geophysics organizations use a broader definition that includes the water cycle including snow and ice; fluid dynamics of the oceans and atmosphere; electricity and magnetism and even problems associated with the moon and other planets. The role of geophysics: Geophysics is applied to societal needs such as mitigation of natural hazards and environmental protection. Without this branch, we can explore earth only by direct observations or drilling. Even drilling has reached a maximum depth of only 12 kms out of 6370 km of earth’s radius. Thus 99.9% of inside earth would have remained unexplored without geophysics. It locates underground water; finds archaeological relics; determines the thickness of glaciers and soil, exploration geophysics has helped us to find the energy sources, also to analyze potential petroleum reservoirs and mineral deposits. Find in the text words whose definitions as follow: ……….: a liquid mixture of hydrocarbons which is present in suitable rock and can be extracted and refined to produce fuels including diesel oil … ………: are pure, solid, inorganic (nonliving) materials found in Earth's crust. They are made of one or more elements that are the most basic, naturally occurring substances on Earth and these elements cannot be broken down (except by radioactive decay). ………..: the study of remains of ancient buildings, etc Insert the best word into the paragraph: physical, gravity, industries, seismic waves, quality, seismic data, hydrocarbons. Geophysicists study the … aspects of the earth using a range of methods, including …, magnetic, electrical and seismic. They play a vital role in the oil and gas … by creating a picture of what lies below the earth's surface. They do this by collecting data on…, which move through and around the earth. Geophysicists are responsible for controlling the … of the … collected and interpreting it in order to create maps of the build-up of…. They also examine the physical properties of rocks, as well as gathering and evaluating well data in order to build reservoir models. 1 Branches of geophysics: It has two main branches (1) solid earth geophysics which uses natural field source to study the earth – their structural variation into crust, mantle and core and the geodynamics, i.e., the plate tectonics. Seismology, Volcanology, geomagnetism… are important branches of Solid Earth Geophysics. It provides the basis of the structure of the earth and the geodynamic balance of the various layers of the earth. Around 8-10% of geophysicists work in this field. The second branch makes use of artificial source and is called Exploration Geophysics. This field was mainly developed for oil exploration and later extended to mineral and ground water exploration. Application of exploration geophysics to oil and mineral exploration made it the fastest developing branch of earth science – almost 90% of geophysicists work in this field. ………….: A branch of science concerned with earthquakes and related phenomena. How is solid earth geophysics different from exploration geophysics? ………………………………………………………………………………………… ………………………………………………………………………………………… Who is the geophysicist? A geophysicist is someone who studies the Earth using gravity, magnetic, electrical, and seismic methods. Some geophysicists use these methods to find oil, iron, copper, and many other minerals. Some evaluate earth properties for environmental hazards and evaluate areas for dams or construction sites. Research geophysicists study the internal structure and evolution of the earth, earthquakes, the ocean and other physical features using these methods. Divisions of geophysics: Geophysics covers a broad range of earth science and offers a variety of options. Here are some, but not all, of the divisions of geophysics: Seismologists, Marine geophysicists, Petroleum geophysicists, Mining geophysicists, Environmental geophysicists, Atmospheric physicist, Gravity geophysicist, Magnetic geophysicist, Electromagnetic geophysicist, Electrical geophysicist, Exploration geophysicists… Petroleum geophysics: The largest number of geophysicists find employment in the petroleum industry. Petroleum geophysicists find oil and gas by building a clear picture of what is below the Earth's surface. A seismic source is used to create shock waves that reflect off the rock layers. The upcoming energy is received by the receivers, and the signal is transmitted through the cable to the recording truck. The signal is digitally recorded and stored on disk. Petroleum geophysicists usually specialize in the acquisition, processing or interpretation of seismic data. Petroleum geophysicists can be divided into three categories: Acquisition Geophysicists that take 'pictures' of the subsurface; Processing Geophysicists that develop and sharpen the 'picture' and Interpretation Geophysicists that use the sharpened 'picture' to construct the shape of petroleum deposits. The most common and effective method of obtaining a clear picture of the Earth's subsurface is the 2 seismic method. In terms of cost management, however, gravity and magnetic data can provide a cost-effective means to assist in interpreting basin to lease-scale structural geology and depth to basement studies at the oil and gas exploration stage. At the reservoir scale, geophysics, in particular, seismic data often provide the primary information on reservoir or aquifer extent. High resolution 3D seismic survey has proven effective in reducing the risk of dry holes and in predicting drilling hazards such as faults and overpressure. 1. Discuss the following questions: A. What do geophysicists need in order to study the earth? B. Count some of the geophysicists’ roles. C. How are geophysicists affective in the oil and gas industry? D. What do you know about the physical properties of the rocks? E. Do you think that the largest number of geophysicists find employment in the petroleum industry? Justify. 2. Fill in the gaps with the appropriate word: seismic data, physics, the seismic method, the acquisition, In the petroleum industry, the most common and effective method of obtaining a clear picture of the Earth's subsurface is... This technique is based on principles of Earth…. Shock waves set off at the surface penetrate the earth like sonar and the returning echo can be used to tell what is below. Petroleum geophysicists usually specialize in…, processing or interpretation of…. However, most will have a good knowledge of the other areas, as well as geology and some engineering principles, as there is a high degree of collaboration between the different groups. 3. Guess to what the following definitions refer: A study of dynamic forces or processes within the earth. The study of the earth, the materials of which it is made, the structure of those materials and those processes. An important part of it is the study of how earth’s materials, structures, processes and organisms have changed over time. The general characteristics of sediments, rocks and rock types present in a stratigraphic division of earth. In other words the study of rocks and their formation. 4. Define/ explain briefly the following from your own background: Earthquakes; marine geophysicists. Good luck 3
